1. Field of the Invention
The present invention relates to a method for manufacturing a magnetic head for recording information on a magnetic recording medium in the form of a direction of magnetization.
2. Description of the Related Art
In recent years, as computers have become popular, a large quantity of information has become dealt with in daily life. Such information is recorded on a recording medium in the form of a large number of physical marks by an information recording/regeneration apparatus, and the recorded information is regenerated by the information recording/regeneration apparatus reading the marks on the recording medium and generating electrical regeneration signals.
One of the information recording/regeneration apparatus is a hard disk drive (HDD), which is characterized by its large storage capacity and high access speed to information. In general, the HDD comprises a magnetic disk with a surface made of a magnetic material, which constitutes a recording medium, and a magnetic head for recording information in the magnetic disk or regenerating the information recorded in the magnetic disk.
The surface of the magnetic disk is magnetized on a small region (1-bit region) basis, and 1 bit of information is recorded in a 1-bit region in the form of a direction of magnetization.
In general, the magnetic head has a coil shaped like a thin film and is disposed close to the magnetic disk. A current is supplied to the coil in the magnetic head to generate a magnetic field, and the magnetic field is leaked to the outside. The leaked magnetic field causes magnetization of each small region of the magnetic disk, whereby the information is recorded in the magnetic disk.
The surface recording density of the magnetic disk increases from year to year, and accordingly, the magnetic head becomes required to have a higher information recording performance. For example, it is required to increase a recording frequency to further increase an information transfer rate in recording information in the magnetic disk by the magnetic head. In order to attain such an increased transfer rate, a distance between turns of a conductive material constituting the coil in the magnetic head is preferably reduced to reduce a length of a yoke portion, that is, a portion between a recording gap and a connected portion (back gap) between an upper magnetic pole and a lower magnetic pole. Thus, a time lag between the generation of the magnetic field in the coil and the recording of the information in the magnetic disk is reduced, whereby a high frequency recording can be accomplished.
On the coil in the magnetic head, an overcoat layer made of an insulating material containing a metal element, such as alumina (Al2O3), is formed by sputtering, evaporation or the like to prevent a current leakage.
Now, in a process for manufacturing the magnetic head, a step of forming the overcoat layer made of Al2O3 on the coil by sputtering will be described by referring to FIG. 16.
Part (a) of FIG. 16 is a cross-sectional view of a part of the coil in the magnetic head, and part (b) of FIG. 16 is a cross-sectional view of the same after the overcoat layer made of Al2O3 is formed on the coil shown in part (a) of FIG. 16.
In a step of forming the coil shown in part (a) of FIG. 16, a spiral coil 70 made of Cu is formed on an insulating layer (not shown) by plating.
In a step of forming the coil shown in part (b) of FIG. 16, an overcoat layer 81 made of Al2O3 is formed by sputtering on the coil 70 formed in the step shown in part (a) of FIG. 16.
As described above, if the distance between turns of the copper wire constituting the coil 70 is reduced to reduce the length of the magnetic pole yoke for a higher write rate in the recording of the information in the magnetic disk by the magnetic head, it becomes difficult to completely fill gaps between the turns of the copper wire with Al2O3, and thus, a void 82 may occur as shown in part (b) of FIG. 16. If such a void 82 occurs, the coil 70 is corroded (oxidized) and an electrical resistance thereof increases, which may cause an increase of the voltage applied to the coil, increase of heat generation in the coil, for example.
Thus, there is known a technique of applying, to a coil, a photoresist, which is a kind of insulating material which has a higher flowability than the insulating material containing a metal element, such as Al2O3, and subjecting the photoresist to a thermal treatment or UV (ultraviolet) treatment to cure the photoresist, thereby forming a photoresist layer on the coil.
FIG. 17 is a cross-sectional view of a conventional magnetic head having gaps between turns of the conductive material constituting a coil filled with a photoresist.
The magnetic head shown in FIG. 17 is a combined magnetic head 32 composed of a regenerating head 10 and a recording head 90.
The regenerating head 10 of the combined magnetic head 32 comprises an element portion 11, a regenerating lower shield 12 and a regenerating upper shield 13 disposed to sandwich the element portion 11 from both sides thereof in a thickness direction, and a regenerating gap layer 14 disposed to fill a space between the regenerating lower shield 12 and the regenerating upper shield 13 and sandwich the element portion 11 from both sides thereof in the thickness direction.
The regenerating upper shield 13 of the regenerating head 10 serves also as a lower magnetic pole of a recording head 90 described later. Therefore, in the following description, the lower magnetic pole is assigned the same reference numeral 13 as the regenerating upper shield 13, and referred to as a lower magnetic pole 13.
The recording head 90 of the combined magnetic head 32 comprises the lower magnetic pole 13, a lower tip secondary magnetic pole 91a and a back gap 91b formed on the lower magnetic pole 13, an insulating layer 92 also formed on the lower magnetic pole 13, a lower coil 93 formed on the insulating layer 92, a lower photoresist coat layer 94 formed to cover the lower coil 93, a lower overcoat layer 95 formed on the lower photoresist coat layer 94, and a recording gap layer 96 formed on the lower overcoat layer 95 and the lower tip secondary magnetic pole 91a. In addition, the recording head 90 has two layers of coils and further comprises an upper coil 97 formed on the recording gap layer 96, an upper photoresist coat layer 98 formed on the upper coil 97, and an upper magnetic pole 99 formed on the upper photoresist coat layer 98 and the recording gap layer 96.
The lower magnetic pole 13 and the upper magnetic pole 99 are connected to each other by the back gap 91b disposed at the center of the lower coil 93 and the upper coil 97 and form a magnetic circuit surrounding the lower coil 93 and the upper coil 97. The magnetic field generated by the lower coil 93 and the upper coil 97 passes through the lower magnetic pole 13 and the upper magnetic pole 99 and is leaked to the outside via the lower tip secondary magnetic pole 91a formed on the lower magnetic pole 13 and the upper magnetic pole 99. The lower tip secondary magnetic pole 91a and the upper magnetic pole 99 each face the magnetic disk, not shown, and the magnetic field leaked to the outside causes the magnetization of each small region of the magnetic disk to be inverted.
With the combined magnetic head 32 shown in FIG. 17, as described above, the photoresist, which is a kind of insulating material, has a higher flowability than the insulating materials containing a metal element. Therefore, the spaces between the turns of the conductive material constituting the coil can be filled with the photoresist without any void, and the problem that the electrical resistance of the coil is increased due to the corrosion of the coil can be avoided.
Comparing the photoresist with the insulating material containing a metal element, however, the photoresist generally has a lower thermal conductivity than the insulating material containing a metal element. For example, the thermal conductivity of the photoresist is about one-tenth of that of Al2O3, which is one of insulating materials containing a metal element. Therefore, with the magnetic head with the photoresist layer formed to cover the coil, a heat generated in the coil when a current is passed therethrough is hard to release, and thus, a trouble with the coil due to the heat generation, such as oxidization and break thereof, is likely to occur.
In view of the circumstances described above, an object of the present invention is to provide a method for manufacturing a magnetic head that enables manufacture of a magnetic head with gaps between turns of a conductive material constituting a coil being filled with an insulating material without any void and heat generation in the coil being suppressed.
In order to attain the object, a method for manufacturing a magnetic head according to the present invention comprises:
a coil forming step of forming a spiral coil made of a conductive material on a predetermined plane;
a resist applying step of applying a photoresist to whole of the coil formed in the coil forming step to fill a gap between turns of a conductive material constituting the coil with the photoresist;
an exposure step of exposing to light a part of the photoresist applied in the resist applying step which covers the conductive material constituting the coil formed in the coil forming step;
a development step of subjecting the photoresist exposed to light in the exposure step to development to remove the part of the photoresist applied in the resist applying step which is exposed to light in the exposure step;
a resist curing step of curing the photoresist remaining after the development in the development step; and
an insulating metal compound layer forming step of forming an insulating metal compound layer made of an insulating material containing a metal element on the photoresist cured in the resist curing step and the coil formed in the coil forming step.
In the method for manufacturing a magnetic head according to the present invention, the photoresist with a higher flowability than the insulating material containing a metal element is applied to the coil, and therefore, the gap between turns of the conductive material constituting the coil can be filled with the photoresist, which is a kind of insulating material, without any void.
In the method for manufacturing a magnetic head according to the present invention, the part of the photoresist applied to the coil which covers the conductive material constituting the coil is removed by exposure and development, and the insulating metal compound layer, which is made of an insulating material containing a metal element and having a higher thermal conductivity than the photoresist, is formed on the conductive material. Thus, heat generated in the coil is released via the insulating metal compound layer in contact with the coil. Therefore, heat generation in the coil can be suppressed.
In the method for manufacturing a magnetic head according to the present invention, the exposure step may be to expose to light a part of the photoresist applied in the resist applying step which fills the gap between the turns of the conductive material constituting the coil formed in the coil forming step, instead of to expose to light the part of the photoresist applied in the resist applying step which covers the conductive material constituting the coil, and
the development step may be to remove a part of the photoresist applied in the resist applying step which is not exposed to light in the exposure step, in stead of to remove the part of the photoresist applied in the resist applying step which is exposed to light in the exposure step.
In general, the photoresist is known to include a so-called positive photoresist, a part of which exposed to light is removed by development, and a so-called negative photoresist, a part of which not exposed to light is removed by development. In the method for manufacturing a magnetic head according to the present invention, either the positive photoresist or negative photoresist can be used. Also in the method for manufacturing a magnetic head using the negative photoresist, the part of the photoresist covering the conductive material constituting the coil can be removed by exposure and development as in the method for manufacturing a magnetic head using the positive photoresist described above.
Furthermore, the method for manufacturing a magnetic head according to the present invention preferably further comprises a small quantity exposure step before or after the exposure step, in which whole of the photoresist applied in the resist applying step is exposed to light with a light exposure lower than that in the exposure step.
With the method for manufacturing a magnetic head including the small quantity exposure step, the part of photoresist which fills the gap between the turns of conductive material constituting the coil and is not exposed to light in the exposure step is exposed to light with a low light exposure, and the thickness of the entire photoresist is reduced in the development step depending on the light exposure. Thus, the thickness of the photoresist can be brought close to the thickness of the coil by adjusting the light exposure in the small quantity exposure step.
As a result, in the subsequent insulating metal compound layer forming step, the insulating metal compound layer made of an insulating material containing a metal element can be formed on the coil without any void with higher reliability, and thus, a magnetic head can be provided in which the heat generated in the coil is readily released and heat generation in the coil is further suppressed.
The method for manufacturing a magnetic head according to the present invention preferably further comprises a dry-etching step before or after the resist curing step, in which whole of the photoresist applied in the resist applying step is subjected to dry-etching.
With the method for manufacturing a magnetic head including the dry-etching step, the thickness of the photoresist is reduced depending on the amount of the etching performed on the photoresist remaining after the development. Thus, by adjusting the amount of the etching, the thickness of the photoresist filling the gaps between the turns of the conductive material constituting the coil can be adjusted and the thickness of the photoresist can be brought close to the thickness of the coil.
As a result, as in the method for manufacturing a magnetic head including the small quantity exposure step, the insulating metal compound layer can be formed on the coil without any void with higher reliability, and a magnetic head with heat generation in the coil being further suppressed can be provided.
The method for manufacturing a magnetic head according to the present invention may further comprises a polishing step of polishing and flattening the insulating metal compound layer formed in the insulating metal compound layer forming step.
With the method for manufacturing a magnetic head including the polishing step, the insulating metal compound layer can be flattened by a polishing method, such as chemical and mechanical polishing (CMP). For example, a magnetic pole layer with a fine pattern can be formed precisely on a surface of the flattened insulating metal compound layer.